The chemistry behind the modern day battery


The dry cell

The dry cell

Often the ammonia produced from the above reaction builds up at the cathode. This tends to insulate the cathode and prevent any electron flow. A few more seconds of use can be had from the battery if it is heated slightly.

Why is heating effective?


The dry cell is used in torches, portable radios, calculators and many more portable electronic items. The word "dry" is very misleading for without water the dry cell could not work. The oxidation half reaction is given below.

The reduction reaction is somewhat complex but it involves the reduction of manganese(IV)oxide to manganese(II) ion.
Below are the reactions involved with the reduction process.

At the cathode the following reaction takes place and represents the reduction reaction.

The hydrogen produced is quickly oxidised to water according to the following equation.
Which of the above reactions occurs at the +ve electrode of the dry cell and which one occurs at the -ve electrode?
Write the overall reaction that occurs in the dry cell
Continue with the lead acid accumulator